1. Field of the Invention
The present invention relates to a rotation detecting sensor comprising a detecting element for detecting rotation of a rotary body as a change in magnetic flux and outputting an output signal corresponding thereto, initializing means for effecting an initialization including at least a gain adjustment for obtaining a desired gain as an initial value based on variation in the output signal upon lapse of a predetermined number of rotations of the rotary body, means for amplifying said output signal together with said gain to provide an amplified signal, and pulse generating means for generating a pulse corresponding to the rotation of said rotary body based variation in said amplified signal amplified based on said gain.
2. Related Art
A rotation detecting sensor of the above-noted type is designed for detecting change in a magnetic flux which occurs in association with rotation of a rotary body. More particularly, as shown in FIG. 4, such rotary body 7 includes a number of teeth 8 along its outer periphery and detecting elements 1 constructed as Hall elements, magnetoresistive elements or the like are disposed at operatively appropriate positions relative to the rotary body. Then, output signals from the detecting elements are used for determining e.g. a rotational speed, a rotational direction of the rotary body.
More particularly, this rotation detecting sensor utilizes change in the magnetic flux on detecting surfaces of the detecting elements which change occurs in association with rotation of the rotary body. The detecting elements detect this magnetic flux change and convert it into an amplitude-variable electric signal corresponding thereto. Then, this output signal is inputted to a logical determining section 4 in which the output signal is e.g. binarized through an arithmetic logical operation, thus converted into a pulse corresponding to e.g. the detected rotational speed of the rotary body.
The rotation detecting sensor normally comprises the magnetism detecting elements 1 and a single integrated circuit for effecting amplification, offset adjustment and pulse generation.
According to a recent version of the above type of rotation detecting sensor now commercially available, in order to extend its detection distance (i.e. to obtain greater freedom in the choice of the separating distance between the teeth 8 of the rotary body and the magnetism detecting elements 1), within a period delimited by power-ON (energization) of the sensor and occurrence of a predetermined number of amplitude variations subsequent thereto (specifically at a predetermined rotational speed of the rotary body when it is being rotated), the sensor automatically effects a gain adjustment and/or an offset adjustment on the signal to be inputted to the logical determining section so that an appropriate threshold value may become available for use in a logical threshold processing operation in the logical determining section.
The gain adjustment is effected for automatically obtaining such an appropriate gain as will result in a signal having an appropriate intensity confined within a predetermined range. Whereas, the offset adjustment is effected for automatically obtaining such an appropriate offset value as will result in a signal having an appropriate median amplitude value within a predetermined range.
In effecting “initialization” exemplified by the gain adjustment and the offset adjustment described above, determination of the timing for effecting this process relies upon the counted number of cycles of the signal.
Incidentally, one possible application of such rotation detecting sensor is its use in a vibrating machine body such as an automobile body. In such case, the vibration of the machine body per se such as the automobile body can cause a periodic change in the separating distance between the rotary body and the detecting element even when the rotary body is not rotating. Or, a small periodic rotational vibration can occur in the rotary body due to the vibration of the machine body These cause a change in the magnetic flux, so that the sensor may generate an inadvertent output signal based on such vibration, not on rotation of the rotary body.
Then, if the initialization is effected under such condition in the presence of inadvertent vibration-associated variation (i.e. vibration noise) in the output signal from the detecting element, the gain adjustment will result in an excessively large gain, since the vibration noise is a very small change in the magnetic flux.
Thereafter, when the rotary body is actually rotated, the sensor picks this up as a sufficiently large magnetic flux. Hence, when this output signal is amplified together with the excessively large gain previously obtained, the resultant amplified signal will have a value exceeding a maximum signal processing range of the integrated circuit. Then, if the pulse generation is effected under this condition, there will occur such inconvenience as disturbance in the pulse generation timing.
As a solution to such problem, it is conceivable to reduce the sensitivity of the sensor or increase the separating distance between the rotary body and the detecting element. Obviously, such solutions are undesirable because of disadvantageous reduction in the sensor sensitivity.
Another solution has been proposed which detects or monitors stop condition of the rotary body (which occurs e.g. when the automobile body is stopped) continued for a predetermined period and then effects an initialization again thereafter. With this solution, however, the initialization is effected when it is not actually needed. Hence, there is the possibility of disturbance in the output pulse while the initialization is being effected.
Still another solution has been proposed (see patent reference 1: Japanese Patent Application “Kokai” No.: 2000-205259, its claim and FIG. 1) which provides e.g. a “displacement sensor” separately for detecting the physical vibration (i.e. another sensor dedicated for detection of vibration, not rotation), so that the output of the rotation detecting sensor may be appropriately compensated for based on the vibration detection by this displacement sensor. This solution is also disadvantageous or not practical because of significant cost increase expected from the provision of the additional sensor.
Next, what happens if such erroneous initialization is effected in the presence of vibration noise will be described in greater details with reference to FIGS. 4, 5,6 and 7.
FIG. 4 is a functional block diagram of a conventional rotation detecting sensor. FIG. 5 is a flowchart illustrating initialization and detection operation effected by the rotation detecting sensor shown in FIG. 4. FIG. 6 is a diagram showing amplified signal and its associated output pulse waveform (output pulses) when the initialization is effected based on an amplified signal from the detecting element resulting from vibration.
Referring first to FIG. 4, the conventional rotation detecting sensor includes a pair of detecting elements 1, a pre-amplifier 2 for amplifying signals from these detecting elements 1, an offset adjustor 21 for effecting an offset adjustment on the pre-amplified signals, a main amplifier 20 for amplifying the signals after the offset adjustment, a logical determining section 4 for effecting a logical operation on the resultant signals to convert them into e.g. pulses and an output section 5 for outputting the pulses.
In the above, the logical determining section 4 is responsible for generating at least a number of pulses corresponding to rotation of the rotary body 7 and optionally shaping the pulses in accordance with e.g. a rotational direction of the rotary body, so that such shaped pulses may be outputted.
As shown in FIG. 4, when an initialization determining section 3 has determined that a certain condition such as power-ON is satisfied, an offset value to be used by the offset adjuster 21 and a gain value to be used by the main amplifier 20 are obtained in advance by effecting an offset adjustment by the offset adjuster 21 and a gain adjustment by the main amplifier 20.
Conventionally, the gain adjustment is effected only once at the time of power-ON which satisfies the initialization determining condition and the gain value thus obtained is retained as it is to be used subsequently for e.g. amplification of the output signal.
Next, this type of initialization and signal processing subsequent thereto will be described in details with reference to the flowchart of FIG. 5.
(Initialization)
As shown at the upper part of in this flowchart, in response to power-ON, while serially inputting the output signals from the detecting element 1, the process effects an offset adjustment and a gain adjustment (#51-1 and #52) with using the cycle of the signal as a unit therefor. Then, the process effects a logical determination for pulse generation (#53-1) and output of generated pulse (#54-1). This process is continued or repeated until it is judged (#55) the number of outputted pulses exceeds a predetermined number of times (e.g. 6 times). With this initialization, an appropriate gain is obtained.
Therefore, after this initialization, the resultant gain has a value which is appropriate for that particular instance in the process.
(Signal Processing after Initialization)
Upon completion of the initialization, the process goes on to a closed loop shown at the lower part of the chart. In this loop, while inputting new signals, the process obtains amplified signals with using the gain previously obtained through the initialization described above and effects a logical determination and generates and outputs including pulses (#53-2 and #54-2).
As shown, the offset adjustment is effected in each cycle of inputting new signals (#51-2).
The forms of signals processed by the above are illustrated in the diagram of FIG. 6 which shows time along the horizontal axis and shows amplified signals (upper row), undesired output pulse waveform (middle row) and optimal pulse waveform (lower row) all along the vertical direction.
Referring first to the horizontal axis representing time, an area (Area A) shown on the left end and including relatively small (amplified) signals is an area when element output signals due to vibration are being inputted. From the center to the right side of the diagram, there is shown another area (Area B) which is an area when output signals due to rotation of the rotary body are being inputted. The figure includes still another area (Area C) which is included in the Area A at the beginning thereof. This Area C is an initialization area for effecting the initialization.
Referring next to the vertical direction of the diagram, the lowermost row represents the optimal pulse waveform to be obtained from the element outputs. The middle row represents the undesired pulse waveform obtained from amplified signals which were erroneously amplified with using the gain set based on vibration-associated output variation. The upper row represents amplified signals which result in or correspond to the undesired pulse waveform.
Further, within the upper row, a pair of opposed two-dot chain lines denote or delimit together a maximum signal processing range of this sensor. Further, one-dot chain lines denote threshold values for pulse generation. In this diagram both the “appropriate or optimal threshold value” and the “inappropriate threshold value” are denoted with the one-dot chain lines. The “appropriate threshold value” is a threshold value which should be employed in threshold value processing for proper pulse generation even in the presence of a signal which exceeds the maximum signal processing range. Whereas, the “inappropriate threshold value” is an undesirable threshold value which is set relying solely on the maximum signal processing range.
As described above, the pulse waveform shown in the middle row is a pulse waveform obtained by a threshold value processing based on the inappropriate threshold value. Whereas, the pulse waveform shown in the lower row is a pulse waveform obtained by a threshold value processing based on the appropriate threshold value.
Hence, in this prior art, as shown, there exists disagreement between the pulse waveform shown in the lower row and the pulse waveform shown in the middle row.
According to the sensor of the type to which the present invention pertains, the sensor is constructed such that a pulse generation threshold value for delimiting pulse generation timing may be automatically set. More particularly, as illustrated in the pulse generation process in the Area B (rotation) shown in FIG. 6, this pulse generation timing is set as a timing when an amplified signal intersects this pulse generation threshold value (one-dot chain line).
Referring now to FIG. 7, in the process of processing amplified signals having predetermined unit cycle, the above-described pulse generation threshold values are set based on a width or difference Vpp between a maximum value Vmax and a minimal value Vmin of the single unit cycle of amplified signal. More particularly, an upper threshold value VthH and a lower threshold value VthL are set one after another as values which respectively satisfy: e.g. VthH=Vmax−r*Vpp, VthL=Vmin+r*Vpp, where r=0.15.
Namely, these pulse generation threshold values are automatically set based on range (magnitude) of amplitude variation occurring in a unit cycle of the amplified signal.
Referring back to FIG. 6, when the initialization is effected in the presence of vibration-associated signals detected. The amplified signals resulting therefrom have a small signal intensity as shown in the left end of the upper row. Under this condition, if output signals are inputted one after another and the gain adjustment as an example of initialization is effected for obtaining an appropriate gain (i.e. appropriate for such outputs), because of the weak signal intensity, the resultant gain will approximate a maximum gain permissible with this sensor.
If the vibration continues under the above condition, as shown, upon lapse of a predetermined number of amplitude variations thereof, the process automatically effects pulse generation in accordance with the standard sequence. In this condition, however, the hysteresis widths of the pulse generation threshold values are extremely small.
Thereafter, when the rotary body actually begins to rotate, because of the excessively large gain obtained previously, the resultant amplified signals should exceed the maximum signal processing range of the circuit. Consequently, because the pulse generation threshold values employed at this stage are inappropriate, inappropriate pulses will be generated as exemplified by the relationship between the undesirable pulse waveform shown in the middle row and the appropriate pulse waveform shown in the lower row of the FIG. 6.
In the construction of the present invention, as will be described later herein, the pulse generation threshold values are continuously updated and optimized according to the range of the periodic variation in the amplified detection signals, thereby to provide an appropriate pulse waveform. In contrast, with the conventional construction, as shown on the right side in FIG. 6, the generated pulses have a relatively large pulse width as determined by the maximum signal processing range.
As a result, if the sensor detects the rotational speed of the rotary member and effects the predetermined control scheme in the manners described above, proper performance cannot be obtained with this sensor.
In view of the above-described state of the art, a primary object of the present invention is to provide an improved rotation detecting sensor capable of obtaining an appropriate gain through initialization even when this initialization is effected based on a change in output signals from a detecting element due to a factor other than rotation, thereby to generate appropriate signals such as pulses associated with rotation of a rotary member, so that the sensor can provide highly reliable rotation information.